<title>Influence of temperature and free carries on four-wave mixing in semiconductor microcavities</title>

Abstract

In semiconductor microcavities (MCs) with embedded quantum wells (QW) a strong two-dimensional (2D) confinement of the light in the growth direction leads to an enhanced exciton-photon interaction, which results in the formation of mixed exciton-photon states described in terms of quasi 2D-polaritons. The density of these states is strongly reduced compared to exciton one, due to a very small in-plane mass. As a result, one can hope that the high filling of the polariton states near the polariton band bottom can be achieved at relatively small total density without destroying the strong coupling regime. However such a filling never was reached at low excitation density range where the polariton relaxation to the polariton branch bottom is determined by the emission of acoustic phonons. The reason is in the fact that the polariton lifetime is comparable with phonon scattering time. As a result, the energy distribution of polaritons clearly demonstrates 'bottleneck effect' both under the above band gap excitation and the resonant excitation below free exciton level. However the high occupation of polariton states near the band bottom is relatively easy reached under conditions of a strong resonant excitation into the lower polariton (LP) branch at particular wavenumbers close to the inflection point of the LP dispersion. It is explained as the result of stimulated hyper-Raman scattering (or four-wave mixing) of pumped polaritons with (E p, k p) to states with the energy and momentum [E 1, k 1 approximately 0] and [E 2 = 2E p - E 1, k 2 = 2k p], which referred to as the 'signal' and 'idler,' respectively. Here we investigate the influence of a temperature and an additional above band gap excitation on the stimulated scattering in MCs. A GaAs/AlAs MC containing 6 InGaAs quantum wells in the active layer (Rabi splitting Ω of 6 - 7 meV) has been investigated in a wide range of detunings between free exciton level and bottom of the photonic mode from δ = 0 to -3 meV. The resonance excitation into an LP branch was carried out with a tunable Ti-sapphire laser. The HeNe laser was used for the additional above GaAs band gap excitation. The sample was mounted in a helium thermostat with the temperature control at T = 5 - 30 K.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.